The present invention relates to a digital muting circuit, and more particularly to a digital muting circuit for muting sounds or aural data having been subjected to pulse code modulation (PCM) or releasing such muting.
There have been known in the art various digital audio signal recording and reproducing systems where a synchronizing signal, an error check code, and an error correction code etc. are added to audio data (PCM sound data). In these systems, the audio data are usually obtained by applying pulse code modulation to an analog sound signal and generating a block signal of a predetermined format in accordance with a modulation system suitable for recording and reproducing operations. The modulated sound signal thus obtained is recorded on a recording medium.
For such digital audio signal recording and reproducing systems, it is required to mute sound in compliance with intention of a user at the time of reproduction (which is also referred to as "on-mute"), or to release muting state to thereby return to the original sound output state (which is also referred to as "off-mute").
The muting circuit in conventional digital audio signal recording/reproducing systems has applied on-mute or off-mute to a reproduced analog sound signal obtained by applying digital-to-analog conversion to reproduced and demodulated PCM sound data using a D/A converter.
On the other hand, ICs (Integrated Circuits) may be reduced in cost to much extent by mass production. Further, digital ICs have various advantages such that they have resistance to power supply voltage change, noise, temperature change etc., and they are stable in performance in the prolonged use, and permit high reliable and stable operation. For this reason, it is advantageous to construct the above-mentioned muting circuit as a digital circuit, thereby permitting it to be incorporated into the digital IC. Such an implementation can realize non-adjustment.